Consider the following diagram (Section 4 in [1]})
\({E_{{\mathbf {V}}_{\alpha }}\times E_{{\mathbf {V}}_{\beta }}&F_{\alpha ,\beta }[l]_-{\kappa _{\alpha ,\beta }}[r]^-{\iota _{\alpha ,\beta }}&E_{{\mathbf {V}}_{\alpha +\beta }}}.\) 
